Hydraulic actuators



March 25, 1969 s. M. ELLIS 3,434,387

HYDRAULIC ACTUATORS Filed March 2, 1966 Sheet of 3 March 25, 1969 s. M. ELLIS 3,434,387

HYDRAULIC ACTUATORS Filed March 2, 1966 Sheet 7 2 of 3 19 19 p 14 i6 l7 14 4 I74 4 2& Q

March 25, 1969 s. M. ELLIS HYDRAULIC ACTUATORS Filed March 2, 1966 INA/70R ran-"0w. Us

- I. a, A ruck-I nite ABSTRACT OF THE DISCLOSURE A redundant actuator system wherein a plurality of fluid actuator paths are provided with clutch coupling means which allow for disparity in position between the individual pistons of the actuator paths while still allowing the transmission of force thereby. A clutch re-engagement means and a switch indicator means are also provided in the system.

The invention relates to hydraulic actuators and to a parallel redundant hydraulic actuator which is capable of disconnecting elements associated with failed systems without the aid of auxiliary electrical or mechanical ap paratus or auxiliary hydraulic valves.

According to the invention a parallel redundant hydraulic actuator has three or more actuator paths each including an actuator unit, engageable with a common output member so as to be capable of producing rotational movement of the common output member, in which any one of the actuator units may be disengaged from the common output member as a result of a malfunction or other event, including latching means comprising a pivotally mounted member carrying a further pivotally mounted member on each of two arms thereof, the actuator units being so associated with respective portions of arms of the further pivotally mounted members that when a predetermined number of actuator units becomes disengaged from the common output member the pivotally mounted member and the further pivotally mounted members are caused to assume positions such that at least two remaining actuator units are interlocked positively with the common output member, so that disengagement from the common output member of a further actuator unit, even if it were initiated, would be frustrated.

The parallel redundant hydraulic actuator system may include safety means arranged whereby a disengaged actuator unit is prevented from becoming accidentally reengaged with the common output member and whereby a disengaged actuator unit can be re-engaged easily with the common output member when positively controlled to do so.

The foregoing and further aspects of the invention will become apparent from the following description of some preferred embodiments thereof with reference to the accompanying drawings, in which:

FIGURE 1 shows an end elevation, part cut away, of a parallel redundant hydraulic actuator system for producing rotational movement of a common output member;

FIGURE 2 shows diagrammatically a side sectional view of the system of FIGURE 1, for ease of explanation two pairs of actuator units being shown located to one side of the rotational axis of the common output member whereas in fact one pair of actuator units is located on either side of the rotational axis of the common output member;

FIGURE 3 shows an end elevation, part cut away, of a further parallel redundant hydraulic actuator system for States atent O 3,434,387 Patented Mar. 25, 1969 producing rotational movement of a common output member, and

FIGURE 4 shows diagrammatically a side sectional view of the system of FIGURE 3, being of similar format to that of FIGURE 2.

It is to be understood that the illustrations are not of complete systems, only the hydraulic parts being shown. Details of suitable accessory electric circuitry for use with these systems can be had from the specification of our co-pending United States patent application Ser. No. 398,- 612, filed Sept. 23, 1964, and now Patent No. 3,272,090.

Referring firstly to FIGURES 1 and 2 the main part of the actuator is a cylinder block 1 having four cylinders 2, 3, 4 and 5 each containing a double-acting piston 6, 7, 8 and 9 respectively, connected to which are respective piston rods 10, 11, 12 and v13:. Each of the pistons 6, 7, 8 and 9 has associated therewith a separate electricallyoperating position indicator of a kind known per se, not forming part of the invention, and indicated for reference purposes at 15.

Each of the cylinders has a port and a conduit 16 at one end and another 17 at the other end fed from hydraulic pressure supply lines 14 or 14. The flow of pressure fluid to and from the two ends of the cylinders, is controlled by a spool valve 18 of known type. Each spool valve 18 is operated in two way sense by an electric torque servo motor, indicated at 19. Each electric torque servo motor 19 is connected by a spring 20 to its associated position indicator 15 so as to provide low gain mechanical feed back to provide centering when the electrical supply is 0h. The motors 19 are controlled by electrical means (not shown) which also responds to the position signals from the position indicators 15.

The piston rods 10, 11, 12 and 13 are pivotally connected to rotatably mounted members 2.1, each of which forms the input portion of a clutch, the output portions being provided by annular flanges 22 formed on a rotatably mounted common output shaft 23. One clutch output portion 22 is provided for each pair of actuators having a common hydraulic supply. Each clutch input member 21 is clutchably engaged with its corresponding clutch output member 22 by balls 24 which engage in corresponding depressions in the members 21 and 22 and some of which are caged in a slideable auxiliary clutch member 25. Each of the clutch input members 21 are rotatably mounted and biased towards their associated clutch output members 22 by ferrules 26. A fluid pressure is applied to the ferrules 26, to provide the bias for the clutch input members 21, via conduits 27 connected to the two main hydraulic supply conduits 14. Springs 28 are provided to maintain the ferrules 26 in their correct positions when the hydraulic supplies are switched ofi.

The clutch auxiliary members 25 are each biased by a spring 29 (FIGURE 1) to cause them to move upwardly, as shown in the figures, when one of the actuator units fails and the caged balls of the auxiliary clutch member 25 become disengaged from the depressions in their associated input and output clutch members 21 and 22 respectively. This ensures that if after a clutch becomes disengaged due to one of the actuator units failing the piston thereof becomes re-aligned with the pistons of the other actuator units its associated clutch cannot re-engage. A switch 30 (FIGURE 1) is associated with each auxiliary clutch member 25 such that when its associated member 25 is moved out of normal alignment the switch is actuated to provide an alarm (not shown).

Plungers 31, operably engageable with auxiliary clutch members 25 are provided for re-engaging the clutches. The plungers 31 are normally biased away from the menu bers 25 by fluid pressure supplied thereto along conduits 32 supplied from the main hydraulic supply conduit 14. The plungers 31 are actuated to provide re-engagement of the clutches via auxiliary clutch members 25 by fluid pressure supplied by conduits 33 from a supply conduit 34 under control of a re-engagement solenoid valve (not shown).

Latching means is provided in the form of a member 40 pivotally mounted on a flange 35 depending from the common output member 23. On the extremity of each arm of the member 40 is pivotally mounted a further member 36, each arm of each member 36 being associated with a portion of one of the clutch input members 21 such that when the clutches are engaged the members 21 are spaced apart from the arms of members 36 and such that when any clutch becomes disengaged its input member 2.1 moves laterally to engage the associated arms of member 36 causing it to pivot such that its other arm engages its associated clutch input member 21. The arrangement is such that when two clutch. input members 21 have moved due to disengagement of their associated clutches both arms of both members 36 are in engagement with all the clutch input members 21 so that no further disengagement of clutches is possible.

The common output member 23 is rotatably mounted at each of its extremities by a ball race 37 which co-operates with an annular flange 38 on the cylinder block 1 via a liner 37a. The liners 37a are normally restrained by spring loaded pins 39 until friction on the ball races becomes excessive at which time the ball races operate as plain bearings, between liners 37a and flanges 38. When this failure of the ball races 37 occurs the pins 39 are forced out of the apertures in liners 37a against the bias of their spring loading to protrude from the cylinder block 1 to indicate that a fault has occurred in the relevant ball race.

The output from the system is derived from the portion of flange 35 remote from the common output member 23.

The normal operation of the complete system is as follows. Individual and identical power signals are applied to the servo motors 19. These apply appropriate movements to the spool valves 18, which all move in one direction or the other as required. The full hydraulic pressure applied over the lines 14 and or 14' marked P is conducted via the conduit 16 to the ends of the hydraulic cylinders 2, 3, 4 and 5 through which the piston rods project. Due to the movement of the spool valves 18 either the high pressure line 14 or 14' marked P, or the exhaust line 14 or .14 marked E, is connected to the conduits 17. 'If the movement of the spool valves 18 is such as to connect the lines marked P to the conduit 17 then the actuator pistons 6, 7, 8 and 9 all move downwardly in FIGURE 2 because it is arranged that the area of the pistons acted upon at the top sides of the pistons is greater than the areas acted upon by the pressure at the bottom ends of the pistons. Hence, if the line pressure acts upon both ends of the pistons they will always move to force the piston rods downwardly, and as they move hydraulic pressure fluid flows through the conduit 16 from the bottom ends of the cylinders back to the pressure supply lines P. On the other hand, if the spool valves 18 are opened in such a direction as to connect the conduits 17 to the lines 14 or 14' marked B, then the pressure fluid acting at the bottom ends of the pistons 6, 7, 8 and 9 moves them all upwardly. The instantaneous position of each piston in either direction is picked off by the position pick-offs 15 and a position signal is transmitted back to the electrical means (not shown) in each case, so that when each actuator piston has carried out the required movement, the position signal, which opposes the input signal, balances the input signal from the demand means so that the output signal from the electrical means (not shown) to the servo motors 19 is reduced to zero.

The movement of the pistons 6, 7, 8 and 9 is transmitted via their associated piston rods 10, 11, .12 and 13 through the clutch input members 21 to the clutch output members 22 so causing a corresponding rotational movement of the 9 1 I 9 1 output member 23 which can be derived from the end of the flange 35 remote from the common output member 23.

The full hydraulic pressure is always available via conduit 32 to maintain the plungers 31 in their off position and via conduits 27 to act upon ferrules 26 to maintain all the clutches in their engaged positions.

If the hydraulic pressure in one of the supply lines 14 or 14 should fail due, for example, to a pump failure the two ferrules 26 associated with the pair of actuators utilising the failed supply cease to maintain the two associated clutches in engagement. When the pistons of the actuators associated with the hydraulic supply which has not failed are next moved the two pistons associated with the failed supply remain stationary. Hence the balls 24 associated with the clutches of the two failed actuators move out of the depressions in their associated clutch input and output members 21 and 22 and the caged balls are moved upwardly out of alignment with these depressions under the bias of the springs 29 associated with the relevant auxiliary clutch members 25. With the disengagement of the two clutches associated with the failed actuator units, the associated clutch input members 21 move outwardly from their associated clutch output member 22 due to the balls 24 being forced out of the depressions. Hence, the two clutch input members 21 moving outwardly engage the arms of their associated latch member 36 so causing the other latch member 36, due to pivotal movement of member 40, to engage the remaining clutch input members 21 to maintain their associated clutches engaged even upon a further failure occuring.

It will now be assumed that the hydraulic pressure supplies are maintained but one of several other types of failure occurs. The first possibility is a failure in the electrical control means (not shown) for one of the actuator units. The servo motor 19 of the failed control receives no power to cause it to execute any movement subsequent to the failure. The other three units function normally and move the common output member 23. The actuator piston of the failed unit remains in a position in which it was placed by the last signal preceding the failure. The movement of the common output member 23 causes the clutch associated with the failed actuator unit to disengage due to movement of the associated clutch output member 22 relative to the clutch input member 21, this latter member being held against movement with the associated clutch output member 22 due to the full hydraulic pressure supply being applied to the upper surface of its associated piston under control of spool valve 18 which is moved under control of the low gain mechanical feed back centering arrangement. Hence, again the balls 24 ride out of the depressions in the members 21 and 22, the caged balls are moved upwardly due to the spring bias of spring 29 acting on the clutch auxiliary member 25 and the associated clutch input member 21 is moved away from the clutch output member 22 to engage the respective arm of the latch member 36. It will be evident that since the area of the annulus on which the hydraulic pressure acts inside the ferrule 26 is quite small the three properly functioning actuators can easily overcome the resistance to movement of the ferrule 26 concerned, so allowing its associated clutch member 21 to become disengaged. A similar effect results from a failure of the servo motor 19, of any of the control parts, or an electrical failure of the position indicator 15 or a mechanical jamming of an actuator piston in its cylinder.

Referring now to FIGURES 3 and 4 there is shown a parallel redundant hydraulic actuator system for producing rotational movement of a common output member which is similar to the system shown in FIGURES 1 and 2 but has a different clutch arrangement.

In this system each clutch input member 21 is clutchably engaged with its corresponding clutch output member 22 by radially extending members 41, carried by the clutch input members 21, which engage in corresponding depressions in the clutch output members 22. Some of the members 41 are rotatably mounted on the clutch input members 21 and are linked to corresponding latch members 42 associated with each actuator clutch arrangement.

The latch members 42 are each biased by a spring 43 (FIGURE 3) to cause them to move, so causing a corresponding rotational movement of the associated members 41 such that they are moved out of radial alignment with the depressions in the members 22, when one of the actuator units fails and the members 41 become disengaged from the depressions in their associated clutch output member 22. This ensures that if after a clutch becomes disengaged due to one of the actuator units failing the piston thereof becomes re-aligned with the pistons of the other actuator units its associated clutch cannot reengage.

As in the system of FIGURES l and 2 a hydraulic reengagement system is provided for the latch members 42 so that the clutches can be allowed to re-engage when desired.

The operation of this system is identical to that described for FIGURES 1 and 2, with the exception of the clutch arrangements described above, and therefore will not be further described.

A further clutch arrangement (not shown in any drawing) which could be utilised in place of the one shown in FIGURES 3 and 4 has frusto-conical shaped members in place of the radially extending members 41 and depressions of complementary shape provided in the clutch output members 22. In this case each clutch has a latching member in the form of a shim having an annular protrusion which runs in an annular depression in either the clutch input member 21 or the clutch output member 22 when the clutch is in engagement. The shim is biased in a direction normal to the axis of rotation of the clutch members 21 and 22 such that when the clutch disengages the annular protrusion on the shim rides out of its complementary depression and is moved radially out of alignment therewith. The protrusion on the shim is of such thickness as to maintain the two clutch members apart such that the members 41 cannot re-engage the depressions in the clutch output member 22.

The shims are co-operable with the plungers 31 of the hydraulic system for allowing re-engagement of the clutches.

From the foregoing description it will be clear that the effect of the failure, for any reason, of any two of the actuator units and the consequent release of the respective clutches results in the remaining two units being locked in engagement. A failure in one unit is further represented in the left-hand unit of both FIGURE 2 and FIGURE 4 by the position of the spool valves 18, by the position of the arms of pick-offs 15, by the position of the associated clutch auxiliary member 25 and balls 24 (FIGURE 2), by the position of the associated latch member 42 and members 41 and by the associated clutch input members 21 in engagement with their associated latching members 36.

There can never be fewer than two actuator units coupled to the common output member 23. If there are only two left and one of these fails, the other-though probably capable of doing the required work by itself also has to move the failed one, so that possible violent reaction to this further thrust failure is checked.

I claim:

1. In a redundant actuator system, in combination,

a plurality of actuator lanes, each of which includes an hydraulic piston and cylinder unit, a control valve which moves in response to a command signal so as to admit hydraulic fluid to the piston and cylinder unit, and a piston position feedback arrangement a signal from which backs-oif the command signal when the piston is at a position dictated by the command signal,

a common output member,

and coupling means connecting each piston to said common output member, said coupling means including a clutch input member relatively movably connected to a corresponding piston, a clutch output member on said common output member adjacent the input member, said input member being shiftable toward and away from said output member, clutching means interposed between said clutch input and output members and serving to urge said clutch input member away from the output member upon relative movement thercbetween whereby upon predetermined separation between said members the corresponding actuator lane is isolated from the common output member, means yieldably urging said clutch input member toward said clutch output member normally to retain said clutch input and output members in spaced relation to each other which is less than said predetermined separation therebetween.

2. A parallel redundant hydraulic actuator system as claimed in claim 1 wherein said clutching means comprises ball members for reception within indentations in said clutch input and output members,

a slide member in which at least some of the balls are held captive, the slide member being urged by resilient means so that when the balls are freed from one of the pairs of indentations upon disengagement of the clutch the captive balls are moved to a position where they cannot be re-engaged with their associated indentations, and

selectively operable means arranged to move the slide member to a position where the captive balls will re-engage their associated indentations.

3. A parallel redundant actuator system as claimed in claim 2 wherein there are four lanes with two pairs of clutch input members and a single clutch output member for each pair, a first pivotally mounted member having a pair of arms, a further member pivotally mounted on each arm and each further member having a pair of arms adapted to be engaged by a corresponding clutch input member when the latter is disengaged from the common clutch output member therefor to swing the other arm of the pair toward the other clutch input member of the pair of clutch input members, the spacing and dispositions of said first and second members and said arms thereof being such as to prevent any further clutch disengagement when any two of said clutch input members are separated from their clutch output members by said predetermined separation.

4. A parallel redundant hydraulic actuator system as claimed in claim 2 wherein said selectively operable means comprises a hydraulically operable plunger directly operable on the slide member.

5. A parallel redundant hydraulic actuator system as claimed in claim 2 including switch means operable by the slide member when in a position such that the clutch cannot re-engage, the switch means being connectable in an alarm circuit for indicating that a fault has occurred.

6. A parallel redundant hydraulic actuator system as claimed in claim 1 wherein said clutching means comprises a slide member linked with at least some of said protrusions which are rotatably mounted on said slide member, the slide member being resiliently urged such that when the protrusions are freed from the co-operable indentations upon malfunction of the associated actuator unit, the linked protrusions are rotated to a position where they cannot re-engage with the co-operable indentations, and

selectively operable means arranged to move the slide member to a position such that the linked protrusions are rotated to a position where they can reengage the co-operable indentations.

7. A parallel redundant actuator system as claimed in claim 6 wherein there are four lanes with two pairs of clutch input members and a single clutch output member for each pair, a first pivotally mounted member having a pair of arms, a further member pivotally mounted on each arm and each further member having a pair of arms adapted to be engaged by a corresponding clutch input member when the latter is disengaged from the common clutch output member therefor to swing the other arm of the pair toward the other clutch input member of the pair of clutch input members, the spacing and dispositions of said first and second members and said arms thereof being such as to prevent any further clutch disengagement when any two of said clutch input members are separated from their clutch output members by said predetermined separation.

8. A parallel redundant hydraulic actuator system as claimed in claim 6 wherein said selectively operable means comprises a hydraulically operable plunger directly operable on the slide member.

9. A parallel redundant hydraulic actuator system as claimed in claim 6 including switch means operable by the slide member when in a position such that the clutch cannot re-engage, the switch means being connectable in an alarm circuit for indicating that a fault has occurred.

10. In a redundant actuator system including in combination,

a plurality of actuator paths, each of which includes an hydraulic piston and cylinder, hydraulic fluid supply means, and a control valve responsive to command signals for connecting the cylinder to the supply means to impart relatively opposite movements to said piston as commanded,

a common output member for said paths, and

a coupling means for connecting each of said pistons to said common output member, said coupling means including an overriding clutch assembly, and means connected to said hydraulic supply means yieldably urging said clutch assembly into engaged condition, said overriding clutch assembly including a retainer member and a plurality of clutch elements carried thereby, opposing portions of each piston and said output member having indentations therein normally receiving said clutch elements, spring means normally urging said retainer member to carry said clutch members out of alignment with said indentations.

11. The system according to claim 10 including means for selectively moving said retainer member to align said clutch members with said indentations.

References Cited UNITED STATES PATENTS 802,801 10/ 1905 Dunlap 92-68 X 1,009,301 11/1911 Hansen 92-61 X 1,888,092 11/1932 Peterson 92 68 2,556,834 6/1951 Ashton et al. 9l411 X 2,859,592 11/1958 Mercier et al. 3,272,090 9/1966 Ellis 92140 MARTIN P. SCHWADRON, Primary Examiner.

IRWIN C. COHEN, Assistant Examiner.

US. Cl. X.R. 

